What are bridge attacks?
- Author
- CRYPTO PORT Editorial
- Published
- Updated
- Reading time
- 6 min
In short
A bridge moves assets between chains, and because one side holds a large pool of deposits, bridges have repeatedly been among the most attacked components in the ecosystem. Several large bridge-related losses have occurred. For users, the practical response is to bridge only when necessary and not to leave assets sitting there afterwards.
Key points
- Bridges concentrate deposits at a single point
- Key management and message verification are the weak spots
- Several large bridge losses have happened historically
- Bridge only when you must, and do not leave funds parked
Definition
An incident in which the keys guarding a cross-chain bridge's deposits, or the mechanism that verifies cross-chain messages, are compromised and the pooled assets are withdrawn illegitimately.
A bridge typically locks an asset on one chain and issues a representation of it on another. That design concentrates deposits on the locking side, and from an attacker's point of view breaking one pool is far more efficient than targeting users individually.
Two places tend to be weak. One is control of the keys that move the pooled deposits: if signing power sits with a small group, compromising that group moves the funds. The other is the logic that verifies events on the other chain — a flaw there can let representations be issued against deposits that were never made.
You cannot audit a bridge yourself. What you can do is reduce how much bridging you need. Move only what you will use on the destination chain, and move it back when you are done. For long-term holding, consider swapping a bridged representation for the asset natively issued on that chain.
When choosing one, look at whether the key-management model is published, how widely signing power is distributed, whether multiple audits and an active bounty exist, and how long it has run at what size. Cheaper fees on a new bridge are partly a discount for unproven risk.
Watch out for
- · Bridge only the amount you will actually use, and move it back when you are finished
- · For long-term holdings, prefer the natively issued asset over a bridged representation
- · Do not route large amounts through a bridge that does not publish its signer set or audits